1. Field of the Invention
The present invention relates to a method for casting thin metal strip or wire directly from the molten metal by jetting the molten metal under pressure onto the surface of a moving chill body so as to effect quenching and solidification.
2. Description of the Prior Art
As continuous casting methods for producing thin metal strip or wire directly from the molten metal by quenching the molten metal (defined herein as including an alloy) there are known the centrifugal quenching method and the single roll method. These methods involve a step of jetting the molten metal onto the inside or outside circumferential surface of a rotating metallic drum, thereby quenching and solidifying the metal, thus casting a continuous metal thin strip (defined herein as including ribbon and wire) directly from the molten metal. The quenching rate is so high in these methods that it is possible to obtain an amorphous metal insofar as the alloy composition is selected properly. U.S. Pat. No. 4,221,257 discloses one example of the single roll method.
In the single roll method of the prior art, there are three main parameters which are known to require control during the continuous casting process:
(1) the pressure under which the molten metal is jetted;
(2) the moving speed of the chill body (such as a roll, drum or belt); and
(3) the gap between the nozzle and the chill body.
In the process for continuous casting an amorphous metal, it has been customary to set these parameters on the basis of experience considering the shape of the nozzle opening (meaning the length in the moving direction in the case of a slot-shaped nozzle) and the target thickness of the product sheet.
For example, in the manufacture of a sheet about 30 .mu.m thick from a metal alloy of the composition Fe.sub.80.5 Si.sub.6.5 B.sub.12 C.sub.1 (atomic %) by using a 0.8 mm slot, the following three conditions are typically selected:
(1) jetting pressure: 0.22 Kg/cm.sup.2 ;
(2) moving speed: 24 m/sec.; and
(3) gap between the nozzle and the chill body: 0.15 mm.
However, with some kinds of alloy, no matter how the above parameters may be varied, it proves impossible to obtain a thin metal strip of the desired shape and size, or often even to obtain a continuous thin metal strip at all. Nor is this an uncommon situation in either the case of amorphous or polycrystalline metal strips.
For instance, in the production of a thin strip of silicon steel by means of the single roll casting method, a thin strip of good shape and surface quality cannot be obtained even when the casting parameters are set similarly to those for an amorphous alloy. The surface shape of the product thus manufactured is wavy and has longitudinal fractures, and further, the surface is very frequently so oxidized as to be disclosed. Similar phenomena are also found to take place in the case of stainless and carbon steels.
Also, in the case of amorphous alloys it has sometimes been impossible to produce a thin strip of high quality by the mere selection of the above three casting parameters. This is especially true in the case of Fe-based alloys containing a low percentage of Fe, which are generally brittle and have rough surfaces.
Thus, in the single roll method of the prior art, there are innumerable examples wherein a thin metal strip of the desired shape and quality cannot be produced by the mere proper selection of the above three conditions and the size of the nozzle opening.